- 142 - 



width, crossed bj" three to five concentric ligament grooves; teeth 

 numerous, strong, vertical, the series heing straight and continu- 

 ous; inner margin of the valve v;ith short crenulati^ns. 



Dine ns ions .- Right valve ( ty-oe ) : Len~th, 35 mm.; alt., 24 

 ram.; semidiam. , 10 mm.; length of hi/ge, 22 mm. left valve: Length, 

 38 ram.; alt. 25 mm.; semidiam., 12.5 -^-m.; lenp-th of hinge 24 mm. 



Remarks.- A. prephaina is very close to the recent A. auri- 



cula ta lamarck (1) and undoubtedly is in the same direct genetic 



(1). Anim. sans Vert., vol. 6, p. 43, 1819; Reeve, Gonch. Icon,, 

 Area , pi. 6, fig. 35, 1844*. 



series. The 3o™rlen form is smaller, has more numerous, usually 

 finer, lower and more conspicuously nodulated radial ribs and 

 much narrower interspaces. It may be distinguished from the associ- 

 ated Scapharcas by its "auriculate "outline. 



The single poorly preserved valve in the National !.!useum 

 Collection, which was doubtfully referre'I to a\\riculata by Dall, 

 apoears to belong to this species. 



Occurr enc e . - ipy,- er I.'iocene: Bov;den,beris, Bowden, Jamaica. 



